This invention relates to an ink jet recording, and more particularly to method and apparatus for capping the nozzle of an ink jet recording device to record a desired character or figure on a recording medium upon ejection of recording ink droplets on the medium.
An ink jet printer can generally operate to print on cheap normal paper at high speed with extremely low noise without the necessity of developing and fixing processes and can record figures and chinese characters for practical use as output recording equipment for computers and data communication, etc.
Representative ink jet recording systems will now be described from the prior art for better and easier understanding of the present invention.
One ink jet recording system has a record member arranged opposite to the nozzle of a print head, a charging electrode and a deflection electrode installed between the record member and the print head. In recording operation a pump is, for example, used to impart high pressure to recording ink and the nozzle is vibrated to continuously eject ink droplets from the nozzle in this system, and a video signal responsive to the signal from character generator is applied to the charging electrode to thus charge the ink droplets. Then, ink droplets thus charged are deflected by the deflection electrode to be ejected onto the record member to then record the character or figure thereon.
Another electrostatic inking apparatus has an accelerating electrode for producing ink droplets, a deflection electrode for deflecting the ink droplets thus produced and a shield electrode for shielding the motion of the ejected ink droplets thus deflected from external electric field arranged between print head and record member. Minute pressure is imparted, for example, to recording ink by a pump to form a positive meniscus at the end of the nozzle of print head with recording ink in the nozzle. Then, upon recording operation high voltage is applied to the nozzle of the print head so that recording ink is ejected as droplets from the nozzle by strong electric field formed to the accelerating electrode to thus deflect the ejected droplets suitably by the deflection electrode upon reception of signal from a character generator and to then pass the droplets via the shield electrode onto the record member.
Further ink jet recording system employs a piezoelectric converter for imparting impulse wave to a triangular nozzle to continuously eject recording ink droplets from the nozzle outlet by the strength of the impulse wave increased while moving from the big end toward small end of the triangular nozzle to thus form a desired pattern on the record member arranged opposite to the nozzle of the print head.
Still another ink jet recording system operates to rapidly reduce the volume of fluid chamber within a print head provided for storing recording ink therein upon reception of a control signal to impart the kinetic energy produced by this sudden decrease in volume of the chamber to recording ink to thus eject recording ink droplets from the nozzle provided at the print head upon a record member to form desired pattern on the member.
With respect to the ink jet recording system of the above volume change type of a fluid or pressure chamber formed within the print head to eject a recording ink droplet, the following difficulties are raised in practical use around the nozzle portion of the print head:
First, the nozzle of the print head is easily blocked by dried ink in the nozzle and non-use for a period deteriorates the ejecting function of the nozzle of the print head.
Second, dust tends to adhere to the nozzle face of the print head due to moisture of fluid ink around the nozzle.
Third, recording ink is leaked from the nozzle and bubbles and dust are taken into the nozzle of the print head as the result of external causes such as shock, vibration imparted to the print head and environmental change such as temperature, moisture, etc. occurring around the head.
More particularly, if dust adheres to the nozzle outlet or opening of print head, ejected recording ink is partly collided with the dust with the result that the ejected recording ink droplets cannot keep a predetermined constant amount to be maintained. As a result, a dot or the like is formed at an unexpected portion on the recording medium to deteriorate the recording quality on the medium due to the lack of rectilinear advancement of ejected recording ink from the nozzle of the print head. In addition, ejected ink impinged on such dust that is adhered to the nozzle of the print head tends to moisten the vicinity of the nozzle opening of the print head to contaminate the nozzle face of the head with the ink. This is particularly worse in case, for example, that plural nozzles are provided in one print head (such as, for example, seven nozzles are perforated at one print head to be arranged longitudinally), different from the print head having only one nozzle formed thereat. Other nozzles are also affected badly by the contaminated nozzle due to narrow nozzle intervals on the nozzle face of the print head. In another case, impinged recording ink with dust is solidified on the dust so that the dust adhered with ink is gradually enlarged with subsequent ink with the result that the enlarged lump of ink and dust block the nozzle opening of the print head. Then, no recording ink is ejected from such blocked nozzle of the print head upon the recording medium. Although the nozzle opening of the print head is very small, recording ink has volatility including, for example, ethylene glycol, water and coloring matter as main components. Accordingly, if the recording operation is stopped for a long term, ink gradually evaporates, and in the particular case of a multi-nozzle type print head, the amount of evaporated ink is increased to waste the ink. Further, coloring matter in the nozzle of the print head is solidified to thus produce bubbles following the recording operation. In addition, recording ink tends to be ejected due to external causes such as temperature change, atmospheric pressure change, vibration, shock, etc. so that ink thus ejected badly affects the following recording operation such as by the generation of bubbles in the nozzle of the print head.